* I’m going to once again push a fine piece by Charli Carpenter, who makes the very sensible point that we should separate “protecting the norm against chemical warfare” from “protecting innocent civilians.” They are different cases, and imply different actions, different cost-and-benefit calculations.

President Barack Obama (Evan Vucci/Associated Press)

* The case that the administration is making is about chemical weapons. So it should be judged on that basis.

* I agree with those who argue that the United States has a real national interest in upholding the norm against using chemical weapons.

* Not only that, but given the particular goal, the means counts. Therefore, the failure to secure United Nations support, or at least a very large multilateral coalition, is a significant weakness of the case for military action.

* And, yes, one of the reasons to avoid things like this is because once military action begins, the next steps can be very difficult to predict.

* Nevertheless: We’re not talking about an Iraq invasion or a Vietnam here. The risks and the costs to the United States for military action are real and include some severe downside risks that may not be readily apparent, but it’s still not nearly of the scale of what was planned in Iraq 10 years ago, and it helps nothing to pretend it is.

* It counts, too, that Barack Obama has demonstrated a willingness to accept the risks of disengaging from military action in Iraq, Libya and Afghanistan — something presidents including Lyndon Johnson, Richard Nixon and George W. Bush repeatedly failed to do.